In a typical DAC, the digital value is converted to an analog signal level by using each digital bit to generate its equivalent analog level and by summing all such analog levels to produce the resultant analog conversion. An example of a binary digital-to-analog converter is shown in U.S. Pat. No. 3,705,359 issued to Werner Kappes.
In the Kappes patent, a voltage divider is used to create the analog level for each bit of the input digital word. The analog levels are summed by an operational amplifier. Each bit controls whether its associated analog value is applied to the operational amplifier for summing with the other converted bit values.
While the Kappes technique works very well, it is expensive to implement because of the requirement that each bit have a corresponding analog conversion stage. For example to produce sixty four analog levels, six conversion stages are required. A significant cost savings could be realized if the same number of analog levels could be realized with fewer conversion stages.